Valorization Of Organic Wastes Research Articles

Humic Substances from Waste-Based Fertilizers for Improved Soil Fertility

This research explores how different organic waste transformation methods influence the production of humic substances (HSs) and their impact on soil quality. Using olive and orange wastes as substrates, the study compares vermicomposting, composting, and anaerobic digestion processes to determine which method produces the most humic-substance-rich products. The characterization of HSs in each product included analyses of total organic carbon (TOC), humic and fulvic acid content, humification rate, humification degree, and E4/E6 ratio, with HSs extracted using potassium hydroxide (KOH) and analyzed via Diffuse Reflectance Infrared Fourier-Transform (DRIFT) spectroscopy to assess structural complexity. The results revealed that the chemical composition of the input materials significantly influenced the transformation dynamics, with orange by-products exhibiting a higher humification rate and degree. Vermicomposting emerged as the most efficient process, producing fertilizers with superior humic content, greater microbial biodiversity, and enhanced cation exchange capacity, thus markedly improving soil quality. Composting also contributed to the stabilization of organic matter, albeit less effectively than vermicomposting. Anaerobic digestion, by contrast, resulted in products with lower levels of HSs and reduced nutrient content. Aerobic processes, particularly vermicomposting, demonstrated the most rapid and effective transformation, producing structurally complex, stable humus-like substances with pronounced benefits for soil health. These findings underscore vermicomposting as the most sustainable and efficacious approach for generating HS-rich organic fertilizers, presenting a powerful alternative to synthetic fertilizers. Furthermore, this study highlights the potential of organic waste valorization to mitigate environmental pollution and foster circular economy practices in sustainable agriculture.

Mining of thermophilic biosurfactant producers for solid-state fermentation

Solid-state fermentation (SSF) is an emerging technology for organic waste valorisation to marketable bio products. SSF scale-up is hindered by heat transfer problems that could be diminished operating under thermophilic conditions. Compost samples collected from food waste composting facility in a primary school in Barcelona and textile industry sample from Faisalabad Pakistan were subjected to isolation of thermophilic biosurfactant producing microorganisms. Altogether 43 isolates were screened through biosurfactant qualitative screening, but 18 isolates dominated with promising results which were further shortlisted under solid-state culture to select the five significant performers belonging to Bacillus sp., Aspergillus sp., and Streptomyces sp. The performance of the five isolates in SSF was assessed in time course studies in 0.5-L packed bed bioreactor using winterization oil cake (WOC), wheat bran and glucose as substrates combined with wheat straw as support material. All five isolates colonized the substrate well in SSF systems and exhibited considerable glucose consumption and adaptation within the SSF setup. The fermentation extracts indicated promising surface-active properties as observed by emulsification and oil displacement analysis. These findings provide an effective enrichment strategy for screening of thermophilic biosurfactant producers and can aid establishment of the scale up for the enhanced metabolite production.

Life Cycle Assessment as a Catalyst for Embedding Sustainability in Waste Management Practices

The establishment of sustainable campuses acts as a catalyst, fostering a Living Lab environment where active community engagement is crucial. Recognizing the pivotal role of waste management, university campuses prioritize detailed mapping and characterization of organic waste streams. This process paves the way for the identification of alternative scenarios that reduce and divert waste from landfills through valorization routes such as composting and anaerobic digestion. Acknowledging students' pivotal role in shaping sustainable solutions, their perceptions of solid waste separation assume significance. The effectiveness of the current separation system is critical, especially given the monitoring of bin contamination levels, revealing hindrances to organic waste valorization. Life Cycle Assessment (LCA) emerges as a valuable tool for identifying alternative scenarios for waste reduction and diversion, encompassing anaerobic digestion, composting, and waste-to-food strategies. This study centers on evaluating and reshaping student perspectives on organic waste separation and end-of-life waste management through LCA. A comprehensive survey was designed to elucidate current perspectives on the efficiency and communication of the existing waste management system. Student insights into waste separation practices revealed that the major barriers to effective waste management practices on campus include a lack of education and awareness regarding waste separation. The survey findings also underscore the significance of LCA not only in measuring carbon footprints but also in influencing perceptions and behaviors towards sustainable waste management practices. In conclusion, our study contributes to the discourse on embedding sustainability in educational settings, offering valuable insights for institutions aspiring to drive positive change through innovative waste management strategies.

Comprehensive life cycle assessment of garden organic waste valorisation: A case study in regional Australia

This study evaluates the environmental impacts associated with the conversion of garden organic waste into value-added products, namely compost or biochar, employing various processes. Three distinct scenarios are considered: composting garden organic waste followed by screening of oversized materials (CBP), pyrolysis of oversized screenings of compost into biochar AP(I), and in-situ conversion of garden organics into biochar AP(II). A comprehensive Life Cycle Assessment (LCA) was conducted using OpenLCA software and life cycle impact assessment was conducted using Recipe 2016 midpoint methodology. The environmental ramifications of each scenario were assessed, optimising transport distances in AP(II) to achieve a functional unit of one tonne of biochar produced within a cradle-to-gate system boundary. For the first time, this study offers a holistic exploration of the benefits of soil biochar application, extending its scope to climate change mitigation, incorporating the optimisation of transport distance and its influence when scaling up the technology. The results revealed that global warming was increased from 125 kgCO2 eq during composting of garden waste to 232 kgCO2 eq where oversized screenings of compost is converted to biochar at an off-site facility. However, direct conversion of the oversized organic waste to biochar, without composting, showed reduced global warming impact of 56 kgCO2 eq, and is thus the most favourable scenario to limit climate impacts of this fraction of organic garden waste. However, among 18 environmental impact indicators studied, eight indicators were either not influenced or did not significantly increase by transport distance to an off-site pyrolysis facility, while the magnitude of 10 impact indicators increased with transport distance. The insights and methodologies presented in this study hold global relevance, based on an actual case study in regional Australia, offering valuable recommendations for sustainable waste management practices and establishing biochar as a carbon-neutral or carbon-negative solution. The findings contribute to existing waste management knowledge and provide guidance for accessible carbon dioxide removal and soil carbon sequestration technologies.

Comparative assessment of biochar produced from waste biomass in laboratory furnace and industrial screw reactor systems

Biochar is rapidly gaining traction as a commercially viable carbon dioxide removal (CDR) technology that can be applied globally at various scales. However, the vast majority of published research studies have involved laboratory experiments conducted in an inert environment under well-controlled conditions of heating rate, maximum temperature and residence time. To expand the biochar industry within the next decade as a CDR platform, there is a need to understand differences between biochar produced under “ideal” laboratory conditions versus those generated using the same feedstocks in continuous, industrial scale systems. In the present work, biochar was produced from widely available organic waste feedstocks, including mixed cafeteria food waste, blended coffee grounds and chaff, grape pomace and wood pellets, using both a laboratory furnace operated in a nitrogen environment, and a continuously operated commercial system capable of processing up to ∼1 t/day of dry feedstock. High quality biochar (H:C < 0.7) was obtained for all feedstocks converted by both systems, however high variability in volatiles and decomposition rates was observed in the thermogravimetric analysis (TGA) results for industrial scale biochar. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) showed similar morphologies and surface chemistries in both laboratory and industrial scale samples, in agreement with reported literature data. Based on this initial comparative assessment, we conclude that commercially available thermochemical systems have potential as localized organic waste valorization technologies to produce high quality biochar. We identified important control variables that have the greatest effect on the resulting biochar. Despite the reported differences between biochar materials derived from the same feedstock, key properties critical for soil amendment and remediation applications (i.e., H:C, surface area, %Corg, etc.) are reasonably consistent between laboratory and continuously fed equipment typical of commercial-scale systems. Thus, biochar materials obtained from well-controlled laboratory experiments conducted in a pure nitrogen atmosphere can be reasonably representative of biochar produced from the same feedstocks using industrial scale equipment.

Maximizing resource recovery: Anaerobic digestion of residual biomass from essential oil extraction in four aromatic and medicinal plants

The valorization of organic waste through biomethanization presents a sustainable solution for energy production and waste management. In this study, the objective was to investigate the feasibility of anaerobic digestion for recovering extraction residues from essential oil extraction processes of Lavender, Peppermint, Eucalyptus, and Rosemary. Furthermore, the study aimed to evaluate the characteristics of the residual biomass by determining total organic matter and soluble organic matter using standardized protocols. The digestate obtained after anaerobic digestion was characterized for its physicochemical properties and its potential as an organic amendment. Statistical analysis was conducted to evaluate the results. The results demonstrate variations in these characteristics among different plant residues, with eucalyptus exhibiting lower VMO and higher BOD5 compared to other plants. The results of this study suggest promising potential for energy recovery from extraction residues, with an energy yield of up to 300 kWh/ton of waste. However, fermenting mixtures before anaerobic digestion is not recommended. In addition, the physicochemical characterization of the mixture resulting from the two mixtures MRH and MRF (DB digestate) highlights the potential of the digestate as an organic amendment. It also demonstrates the effectiveness of anaerobic digestion in reducing organic matter and enhancing the quality of the digestate. This contributes to sustainable waste management practices and boosts agricultural productivity. Morphological and elemental analyses provide insight into structural and compositional changes during biomethanization. Overall, this research highlights anaerobic digestion as a cost-effective approach to residual waste disposal in essential oil extraction industries. It supports circular economy principles by potentially generating revenue from energy production and organic amendments. This method offers a promising solution for waste recovery strategies in the transformation sector of aromatic and herbaceous plants for energy production.

Circular bioeconomy practices and their associations with household food security in four RUNRES African city regions

Achieving the United Nation’s 2030 agenda which aims, among other goals, to ensure sustainable consumption and production patterns, requires a sustainable resource use model deployed at scale across global food systems. A circular bioeconomy (CBE) model of resource use has been proposed to reuse of organic waste in agricultural production to enhance food security. However, despite several initiatives recently introduced towards establishing a CBE in sub-Saharan Africa (SSA), minimal scientific efforts have been dedicated to understanding the association of CBE practices and food security. This study use data from 777 smallholder farm households from DRC, Ethiopia, Rwanda, and South Africa, to examine associations between three CBE practices (use of organic waste as compost, as livestock feed, and sorting waste) and household food security. Using different regression and propensity score matching models (PSM). Result reveal that using CBE practices more likely adds a 0.203 score of food insecurity access prevalence (HFIAP), 1.283 food insecurity access scale (HFIAS-score) and 0.277 for household dietary diversity score (HDDS) among households using CBE practiced groups. Associations regarding using organic waste as compost are generally positive but insignificant, while those with sorting waste are significantly and consistently negative. Thus, CBE innovations aiming to enhance household food security could prioritize organic waste valorization into livestock feed consider socio economic aspects such as access to land, access to market, education level, using mobile phone, income and city regions where interventions took place. However, prior sorting of waste is necessary to enable effective waste valorization.

Advancements in Bioelectrochemical Systems for Solid Organic Waste Valorization: A Comprehensive Review

Advancements in Bioelectrochemical Systems for Solid Organic Waste Valorization: A Comprehensive Review

Reproductive output and other adult life-history traits of black soldier flies grown on different organic waste and by-products

The interest in mass-rearing black soldier fly (Hermetia illucens) larvae for food and feed is rapidly increasing. This is partly sparked by the ability of the larvae to efficiently valorise a wide range of organic waste and by-products. Primarily, research has focused on the larval stage, hence underprioritizing aspects of the adult biology, and knowledge on reproduction-related traits such as egg production is needed. We investigated the impact of different organic waste and by-products as larval diets on various life-history traits of adult black soldier flies in a large-scale experimental setup. We reared larvae on four different diets: spent Brewer’s grain, ground carrots, Gainesville diet, and ground oranges. Traits assessed were development time to pupa and adult life-stages, adult body mass, female lifespan, egg production, and egg hatch. Larval diet significantly impacted development time to pupa and adult, lifespan, body size, and egg production. In general, flies reared on Brewer’s grain developed up to 4.7 d faster, lived up to 2.3 d longer, and produced up to 57% more eggs compared to flies reared on oranges on which they performed worst for these traits. There was no effect of diet type on egg hatch, suggesting that low-nutritious diets, i.e. carrots and oranges, do not reduce the quality but merely the quantity of eggs. Our results demonstrate the importance of larval diet on reproductive output and other adult traits, all important for an efficient valorisation of organic waste and by-products, which is important for a sustainable insect-based food and feed production.

Valorization of Cork Stoppers, Coffee-Grounds and Walnut Shells in the Development and Characterization of Pectin-Based Composite Films: Physical, Barrier, Antioxidant, Genotoxic, and Biodegradation Properties.

The development of sustainable materials from the valorization of waste is a good alternative to reducing the negative environmental impact of plastic packaging. The objectives of this study were to develop and characterize pectin-based composite films incorporated with cork or cork with either coffee grounds or walnut shells, as well as to test the films' genotoxicity, antioxidant properties, and biodegradation capacity in soil and seawater. The addition of cork, coffee grounds, or walnut shells modified the films' characteristics. The results showed that those films were thicker (0.487 ± 0.014 mm to 0.572 ± 0.014 mm), more opaque (around 100%), darker (L* = 25.30 ± 0.78 to 33.93 ± 0.84), and had a higher total phenolic content (3.17 ± 0.01 mg GA/g to 4.24 ± 0.02 mg GA/g). On the other hand, the films incorporated only with cork showed higher values of elongation at break (32.24 ± 1.88% to 36.30 ± 3.25%) but lower tensile strength (0.91 ± 0.19 MPa to 1.09 ± 0.08 MPa). All the films presented more heterogeneous and rougher microstructures than the pectin film. This study also revealed that the developed films do not contain DNA-reactive substances and that they are biodegradable in soil and seawater. These positive properties could subsequently make the developed films an interesting eco-friendly food packaging solution that contributes to the valorization of organic waste and by-products, thus promoting the circular economy and reducing the environmental impact of plastic materials.

Waste cooking oil and molasses for the sustainable production of extracellular lipase by Saitozyma flava.

Organic waste valorization is one of the principal goals of the circular economy. Bioprocesses offer a promising approach to achieve this goal by employing microorganisms to convert organic feedstocks into high value products through their metabolic activities. In this study, a fermentation process for yeast cultivation and extracellular lipase production was developed by utilizing food waste. Lipases are versatile enzymes that can be applied in a wide range of industrial fields, from detergent, leather, and biodiesel production to food and beverage manufacturing. Among several oleaginous yeast species screened, Saitozyma flava was found to exhibit the highest secreted lipase activity on pNP-butyrate, pNP-caproate, and pNP-caprylate. The production medium was composed of molasses, a by-product of the sugar industry, which provided nutrients for yeast biomass formation. At the same time, waste cooking oil was employed to induce and enhance extracellular lipase production. After 48h of process, 20g/L of yeast biomass and 150mU/mgdw of lipase activity were achieved, with a productivity of 3mU/mgdw/h. The purified lipase from S. flava showed optimal performances at temperature 28°C and pH 8.0, exhibiting a specific activity of 62U/mg when using p-NPC as substrate.

Green chemistry and biocatalysis: Engineering a sustainable future

The increasing role of biocatalysis in the green and sustainable manufacture of chemicals is discussed. In the last two decades the breadth and scope of biocatalysis has increased enormously as a result of remarkable advances in metagenomics, protein engineering and bioinformatics. Moreover, the use of enzymes has become more cost-effective through advances in immobilization technologies and the application of the immobilized enzymes in continuous flow operation in packed bed reactors. Consequently, biocatalysis is already the method of choice for the synthesis of enantiopure chiral products for the pharmaceutical and fine chemical industries. Further applications in commodity chemicals manufacture are currently being stimulated by the increasing maturity of biocatalysis and the ongoing transition to a bio-based circular economy based on the valorization of organic waste on the road to net zero manufacturing.

Global trends of pyrolysis research: a bibliometric analysis

Pyrolysis has become an interesting waste valorization method leading to an increasing number of research studies in this field in the last decade. The present study aims to provide a comprehensive knowledge map of scientific production in pyrolysis, discuss the current state of research, and identify the main research hotspots and trends in recent years. The systematic review, supported by analysis of countries and institutions, keyword co-occurrence analysis, analysis of keyword trends, journal analysis, and article impact, was carried out on 6234 journal articles from the Science Citation Index Expanded database of the Web of Science Core Collection. As a result, four main research hotspots were identified: 1) characterization techniques and pyrolysis kinetic models, 2) biochar production and its main applications, 3) bio-oil production and catalytic pyrolysis, and 4) co-pyrolysis, which has become a consolidated research hotspot since 2018. Additionally, the main challenges and opportunities for future research have been identified, such as 1) the development of multi-step kinetic models for studying complex wastes, 2) the integration of biochar into other valorization processes, such as anaerobic digestion, and 3) the development of catalytic hydropyrolysis for the valorization of organic waste. This bibliometric analysis provides a visualization of the current context and future trends in pyrolysis, facilitating future collaborative research and knowledge exchange.

Multi-Parametric Analysis Based on Physico-Chemical Characterization and Biochemical Methane Potential Estimation for the Selection of Industrial Wastes as Co-Substrates in Anaerobic Digestion

Anaerobic digestion is considered as one of the most feasible waste-to-energy technologies for the valorization of organic wastes. It can be applied to many different substrates but the mono-digestion of a single substrate usually has some important drawbacks due to the physico-chemical characteristics of the substrate. A feasible solution is the simultaneous co-digestion of several substrates with different composition and characteristics, so that synergetic effects may be generated and physico-chemical characteristics may be compensated, thus reaching higher process efficiencies and biogas production rates. In this work, a multi-parametric analysis for the objective comparison of industrial wastes was developed in order to help with decision making about their suitability as a co-substrate in anaerobic co-digestion. Criteria considered for this analysis included sample composition, C/N ratios, theoretical biochemical methane potential (BMP), and other important issues such as production rates, seasonality, and the distance to the WWTP or pre-treatment requirements. Results showed that, among the 13 evaluated wastes, 2 of them showed a higher potential for being used in anaerobic co-digestion: 1. Fried corn from the snack food industry and 2. Wet fatty pomace from the olive oil industry. Both wastes showed high estimated BMP values, high lipid and carbohydrate content, and C/N ratios in a proper range to improve the low C/N ratio of sewage sludge. Other wastes such as olive pomace (dry), skinless corn (not fried), and grape pomace from the winery industry may also be used as co-substrates. As a conclusion, this procedure based on a selection matrix can be considered as a useful tool to help both producers and WWTP operators to make decisions about the potential applicability of specific industrial wastes as co-substrates in anaerobic co-digestion.

Utilization of Digestate as an Organic Manure in Corn Silage Culture: An In-Depth Investigation of Its Profound Influence on Soil’s Physicochemical Properties, Crop Growth Parameters, and Agronomic Performance

The agricultural valorization of organic waste, including digestate from anaerobic digestion, can be a good tool to remedy the problem of soil depletion by intensive crops. This study was conducted to evaluate the effect of digestate application on the chemical characteristics of the soil, including N, P, and K content, pH, and electrical conductivity, as well as the agronomic performance of forage corn (Zea mays L.). Digestate was applied and incorporated into the soil at different rates (0; 0+ recommended NPK rates; 15, 30, and 60 t dry weight (DW) ha−1). Digestate application at increasing doses improved soil chemical characteristics at harvest, and the application of 15, 30, and 60 t DW ha−1 significantly decreased soil pH by 0.15, 0.23, and 0.39 units, respectively. For electrical conductivity, the average values recorded are 196, 212, and 255 uS m−1, respectively, to 15, 30, and 60 t DW ha−1 doses. A significant organic matter enrichment of the topsoil layer was observed only for treatments receiving 30 and 60 t DW ha−1. Similarly, our results showed that the N, P, and K contents increased significantly with digestate application at both rates compared to the positive control. Morphological characteristics of the corn plants (height, leaf number, and collar diameter) and ecophysiology (stomatal conductance and chlorophyll) increased in a global manner compared to the negative control. Indeed, the obtained results showed that this improvement was not proportional to the applied doses for all analyzed parameters. However, there was no significant difference between the obtained values in amended plants with 15 t DW ha−1 and those in the positive control (recommended dose in NPK). In comparison to this previous one, height, leaf number, and collar diameter increased by 15%, 13%, and 20%, respectively, with a 30 t DW ha−1 dose and by 34%, 20%, and 24% with a 60 t DW ha−1 dose. Concerning the relative chlorophyll content and stomatal conductance, the values recorded in the plants amended with 60 t DW ha−1 are 1.7 and 2.2 times higher compared with the positive control. The fresh biomass, dry biomass, and root length parameters increased proportionally to the applied dose.

Simultaneous biosuccinic production and biogas upgrading: Exploring the potential of sugar-based confectionery waste within a biorefinery concept

The imminent need for fossil fuel independence in EU countries has led to an increased development of organic waste valorisation technologies for the production of biomethane and chemical building blocks, such as bio-succinic acid (SA). In this work, the potential of two confectionery waste, in the form of wastewater (SCWW) or a side-stream rejection (SSCW), as inexpensive carbon sources for simultaneous SA production and biogas upgrading was evaluated for the first time. Both substrates were tested batchwise with evolved Actinobacillus succinogenes cultures at different nutrient conditions, SSCW at 100 g L−1 resulting in the highest titres/productivities (∼80 g L−1 and 1.3 g L−1h−1, respectively). Then, simultaneous biogas upgrading under continuous gas feeding was studied at bioreactor-scale, higher gas residence times and pressurization leading to desirable biomethane purities (>98%). The research here conducted is crucial for the cost-effectiveness and scale-up of the technology along this new waste-based biorefinery concept.

Environmental impact scenarios of organic fraction municipal solid waste treatment with Black Soldier Fly larvae based on a life cycle assessment

Biowaste treatment with Black Soldier Fly (BSF) larvae is an alternative option for organic waste valorization. Its environmental impacts should be assessed and compared with conventional treatment options. The research aims to evaluate the treatment of organic fraction of municipal solid waste (OFMSW) with BSF larvae through a life cycle assessment (LCA). This study employed data inventories from literature and aimed to provide a wide range of production parameter values to identify the potentialities of BSF treatment in the best-case and worst-case scenarios. The SimaPro9, the database Ecoinvent3.5, and the impact assessment method IMPACT 2002+ have been employed for the analysis. A sensitivity analysis of relevant parameters was conducted, considering the avoided impacts that can be obtained thanks to the exploitation of larvae proteins for bioplastics or fishmeal production. Research findings highlight six main environmental impact indicators: respiratory inorganics (kg PM2.5-eq), ozone layer depletion (kg CFC-11-eq), terrestrial ecotoxicity (kg TEG soil), land occupation (m2 organic arable), global warming (kg CO2-eq), and non-renewable energy (MJ primary). The most relevant process generating impacts is BSF breeding, followed by boiling, storage, and OFMSW treatment. The environmental performance is better when the conventional fishmeal substituted, thanks to BSF larvae production, is made from areas 10,000 km far, implementing a 100% renewable energy scenario, reducing the energy consumption by 50%, increasing the lifespan of the equipment to 15 years, and products are employed locally. The current study represents the first attempt to evaluate the global higher or lower environmental impact scenario related to OFMSW treatment through BSF larvae.Graphical

Assessment of Manure Compost Used as Soil Amendment—A Review

Organic waste management is an important concern for both industries and communities. Proper management is crucial for various reasons, such as reducing greenhouse gas emissions, promoting sustainability, and improving public health. Composted manure is a valuable source of nutrients and organic matter that can be used as a soil amendment in agriculture. Some important benefits of using composted manure in agriculture include: improves soil fertility, enhances soil structure, reduces soil erosion, suppresses plant diseases, and reduces reliance on synthetic fertilizers. Composted manure represents one of the most effective methods of organic waste valorization. Its macronutrients and micronutrients content can increase plant yield, without any reported negative or toxic effects on the soil and plants at various application rates. However, improper use of farmyard manure can have negative effects on the environment, such as air pollution from greenhouse gas emissions, soil acidification, and contamination of surface water and groundwater by nitrates and phosphates. The properties of the soil, including aeration, density, porosity, pH, water retention capacity, etc., can be improved by the structure and composition of manure. The slow-release source of nutrients provided by the nutrient content of compost can determine proper plants growth. However, it is crucial to use compost in moderation and regularly test soil to prevent excessive nutrient application, which can have adverse effects on plants and the environment.

Solid Waste Management in Peru’s Cities: A Clustering Approach for an Andean District

There is a great deficiency in the collection and disposal of solid waste, with a considerable amount disposed of in dumps instead of in landfills. In this sense, the objective of this research is to propose a solid waste mitigation plan through recovery in the District of Santa Rosa, Ayacucho. For this, a solid waste characterization plan was executed in eight days, and through ANOVA it was shown that there is a significant difference in means between business pairs except between a bakery and a hotel. Through clustering, zones A and B are highly correlated, reflecting that the amount of organic waste was greater than inorganic waste. In the organic waste valorization plan, the results through ANOVA indicate a significant difference for monthly and daily averages, and the clustering shows the different behavior of each month, drawing attention to August, concluding that the valorization pilot plan is viable due to the contribution of a large amount of organic solid waste to the valorization plant.

Promoting the Circular Economy on an Island: Anaerobic Co-Digestion of Local Organic Substrates as a Possible Renewable Energy Source

The local waste co-digestion is an interesting option to tackle in reduced and isolated areas like the islands. The islands have limited territory and scarce fuel production. Moreover, organic waste can create serious environmental problems in soil, water and air. Anaerobic co-digestion (AcoD) is a technology fulfilling the concept of waste-to-energy (WtE) based on local resources. The valorisation of organic waste through AcoD on an island would prevent environmental impacts, while being a source of renewable energy. In this study, cow manure (outdoor and indoor), pig slurry, bird manure, kitchen waste, sewage sludge and oily lacteous waste produced on Island Terceira (Portugal) were tested in mesophilic -35 °C- Biochemical Methane Potential (BMP) co-digestion assays. The goals were to analyse the recalcitrant and high potential produced waste and to estimate the energetic supply source on the island. The cow manure and pig slurry were used as inocula and specific methanogenic activities (SMAs) were carried out. The results showed that both substrates have a significant methanogenic activity-SMA 0.11 g-COD/(g-VSS.d) and 0.085 g-COD/(g-VSS.d), respectively. All the studied combinations were feasible in AcoD, showing TS removals in the range of 19-37%; COD removals in the range 67-78% and specific methane yields from 0.14 to 0.22 L/gCOD removed, but some differences were found. The modified Gompertz model fitted the AcoD assays (R2 0.982-0.998). The maximum biogas production rate, Rmax. was highest in the AcoD of Cow+Pig+Oily and in the Cow+Pig+Sludge with 0.017 and 0.014 L/g-VSadded.day, respectively, and the lowest in Cow+Pig+Bird with 0.010 L/g-VSadded. In our AcoD studies, the bird manure limited the performance of the process, since it was recalcitrant to anaerobic degradation. On the other hand, the oily lacteous waste showed a great potential in the anaerobic digestion. The estimated biogas production, from the best-studied condition, could cover the 11.4% of the energy supply of the inhabitants. These preliminary results would prevent the environmental impact of organic waste on the island and promote the use of local waste in a circular economy scenario.